Rapid, simple, and quantitative techniques have been developed for separation of the envelope, core, and RNP components of a representative type-C oncornavirus. The most recent subject in a series of biochemical studies of these subcomponents of AMV has been to probe for the presence of DNA within the internal core structure by measuring priming activity. Although core preparations retained only 10 percent of the viral protein, they contained over 70 percent of the DNA found in the companion virion preparations. Even if the DNA is of cellular origin, the necessary excision of DNA and packaging within the core may reflect an important action of the tumor virus on the host cell.